This invention relates to a belt portion structure suitable for use in a rough road radial tire. More particularly, the present invention is concerned with a heavy-duty pneumatic tire adapted to prevent the separation of the end of the belt layer without lowering the resistance to heat build-up.
Generally, travelling on rough roads tends to cause various kinds of damage to the surface of the tread of a tire due to the action of gravel, tiles and pebbles, and crushed stone, etc.
For this reason, the tread portion of a tire for use in travel on rough roads is made of rubber different from the tread rubber of a tire for use in travel on a paved high-speed road. That is, it is made of rubber comprising a special blend which has excellent chipping resistance but sacrifices the resistance to heat build-up to some extent.
However, the conventional rough road tire has a plurality of belt layers laminated on top of another and disposed in the tread portion in a circular form in the circumferential direction of the tire of which the outermost belt layer has a width narrower than that of the belt layer adjacent to the undersurface thereof as in the tire for use in travel on an ordinary paved high-speed road, which leads to the occurrence of the separation of the end of the belt layer due to occurrence of penetrating cuts from the tread surface under severe working conditions of travel on rough roads.